Aging is associated with a progressive decline of muscle mass, quality, and strength, a
condition known as sarcopenia. Although this term is applied clinically to denote
loss of muscle mass, it is often used to describe both a set of cellular processes
(denervation, mitochondrial dysfunction, inflammatory and hormonal changes) and
a set of outcomes, such as decreased muscle strength, mobility, and function, a
greater risk of falls, and reduced energy needs.
Resistance training combined with amino acid-containing supplements is an
effective candidate to prevent age-related muscle wasting and weakness
In
particular, sarcopenia has been most attenuated by treatment with many essential
amino acids plus high leucine. In addition, many researchers have focused on
inhibiting myostatin to treat various muscle disorders such as muscular dystrophy,
cachexia, and sarcopenia. Furthermore, more recent studies have indicated the
possible application of new supplements (e.g. ursolic acid) to prevent muscle
atrophy.
Although there are significant increases in strength among
elderly males given high doses of testosterone, the potential risks may outweigh the
benefits. Risks associated with testosterone therapy in older men include sleep
apnea, thrombotic complications, and the increased risk of prostate cancer.
These side effects have driven the necessity for drugs that demonstrate improved
therapeutic profiles. Novel, non-steroidal compounds, called selective androgen
receptor modulators, have shown tissue-selective activity and improved pharmacokinetic
properties. Whether these drugs are effective in treating sarcopenia has yet
to be shown. Dehydroepiandrosterone (DHEA) is marketed as a nutritional supplement
in the USA and is available over the counter. Unlike testosterone and
estrogen, DHEA is a hormone precursor that is converted into sex hormones in
specific target tissues. However, supplementation of DHEA in aged men and
women results in an increase in bone density and testosterone and estradiol levels,
but results in no changes in muscle size, strength, or function.
Because of their combined anabolic effects on skeletal muscle and appetite,
ghrelin and low molecular weight agonists of the ghrelin receptor are considered
attractive candidates for the treatment of cachexia. For example, Nagaya et al. [48]
gave human ghrelin (2 μg/Kg twice daily intravenously) for 3 weeks to cachexic
patients with chronic obstructive pulmonary disease in an open-label study. After
ghrelin therapy, significant increases from baseline measurements were observed
for body weight, lean body mass, food intake, hand grip strength, maximal inspiratory
pressure, and the Karnofsky performance score [48]. In another unblinded
study, the same group demonstrated that treatment with human ghrelin (2 μg/Kg
intravenously, twice daily for 3 weeks) significantly improved several parameters
(e.g., lean body mass measured by Dual-energy X-ray Absorption and left ventricular
ejection fraction) in 10 patients with chronic heart failure
Protein Supplementation
Unfortunately, they conducted the examination of total muscle cross-sectional areas by only magnetic
resonance imaging, and did not perform a detailed morphological analysis (crosssectional area of muscle fiber by biopsy sample). Since the evaluation of muscle
cross-sectional area by magnetic resonance imaging appears to be influenced by the
inner amount of adipose tissue, connective tissue, or water, it is unknown whether
their protein supplementation actually failed to elicit positive effects on the morphometry of muscle fiber.
